Method for fabricating a reflective type reflector plate of a reflective liquid crystal display

ABSTRACT

The method for fabricating reflector plate for a reflective liquid crystal display and the device is disclosed. The present invention includes the formation of a protection layer over the glass substrate having thin film transistors and a layer of transparent electrodes on top, followed by the formation of a layer of undulating resin over the protection layer. If the reflector plate to be produced is a semi-transmissive type, a light-transmitting region is created over the protection layer. Since the protection layer is created in advance of the undulating resin outgrowth, the present method can effectively prevent reflection from the exposure stage during the lithography process, thus the problem of abnormal pattern marks occurring on the reflective surface can be avoided, and the exposure time and the production yield are enhanced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to reflector plates for a reflectiveliquid crystal display and methods for fabricating the same, inparticular to a method for fabricating reflector plates that can preventlight reflections from the exposure stage during the formation ofundulating resin outgrowth, in order to avoid abnormal patternsoccurring on the reflective surface, and furthermore the presentinvention can also shorten the exposure time and increase productionyield.

2. Description of Related Arts

Reflective liquid crystal displays in general employ an external lightsource to illuminate display images. This new type of reflective displaycan effectively reduce the need of using a back light source and canachieve considerable saving on power consumption, making it suitable forportable applications.

Reflective displays in general have a reflector plate on the displaypanel, replacing the conventional back-light portion. These reflectorplates can be further classified into a full reflective type and asemi-transmissive type. The reflective type reflector plate is usuallyequipped with a front-light module which is used to supplement externallight for the necessary illumination on a liquid crystal display. Thesemi-transmissive type reflector plate, like a half-mirror, is able toreceive light from a back-light module in supplement of external lightwhen the ambient light is insufficient. However, display devices havingeither the reflective type or the semi-transmissive type reflector platedo not need the front-light or back-light illumination in the normalconditions, so their power consumption can be reduced. As mentionedearlier, the reflective display having a reflective type reflector plateis usually equipped with a front-light module. When the external lightis insufficient, the display device can switch to the front-light moduleto supplement the ambient light. However, the above-mentioned reflectivelight technology has the shortcoming of noise signals and this is yet tobe solved. As a result, the semi-transmissive type reflector plate ismore favored by users. The semi-transmissive type reflector plate isable to use a back light to supplement the ambient light. This isimplemented by creation of an undulating resin outgrowth on thereflective surface of the reflector plate.

FIG. 7 shows the steps for fabricating a semi-transmissive typereflector plate. A glass substrate (70) is prepared with thin filmtransistors built on top; and, a layer of transparent electricalconductor such as indium-tin-oxide (ITO) is deposited over the surface.Since the glass substrate (70) has thin film transistors formed inadvance of the transparent electrodes, a pixel region is formed inbetween the glass substrate (70) and the transparent electrodes (71)with a gate insulating layer (701) and a protection layer (702).

The transparent electrodes (71) are formed by spin coating a layerpolymer resin on the surface to form a photo-resist layer (72); then thephoto-resist layer is exposed to light in a lithography process toremove photo-resist in areas other than the pattern areas to create aphotomask as shown in FIG. 7 b; then a metal layer as shown in FIG. 7 c,is deposited on the surface to create a reflective film (73); the metaldeposits in the non-pattern areas are removed after photo-etching toform a light transmitting region (74), thus completing the formation ofa reflective type reflector plate with undulating resin outgrowth.

The reflective film (73) can be a single layer or multiple layers offilm. In the case of a 3-layer film, the materials used in differentlayers are molybdenum alloy (Mo), aluminum (Al), and molybdenum alloy(Mo) in that order.

FIGS. 8 a˜c shows the process of fabricating a reflective type reflectorplate, in which the basic steps are similar to those used for asemi-transmissive type reflector plate, except that the step to createthe light-transmitting region is not necessary for the reflective typereflector plate.

In the fabrication of the reflective type reflector plate mentionedabove, it is necessary to point out that the process for fabricating theundulating resin outgrowth over the reflective surface willsignificantly affect the yield rate and the defect rate in theproduction of these reflector plates.

In detailed analysis of the fabrication process, the glass substrate(70) is placed on the exposure stage, and the photomask is precisionaligned and fixed over the light projection areas of the exposure stage,a vacuum pad is then adhered to the bottom of the glass substrate (70)for firming the substrate, and the photo-resist layer is spin coated onthe surface of the glass substrate (70) and exposed under light. In theprocess, the vacuum pad and the protrusion pins will cause lightreflection from the exposure stage, leading to some undesired patternmarks on the surface due to uneven exposure of the photo-resist layer.The pattern marks still exist in a subsequent fabrication process of thereflective film (73). The pattern marks reflecting the shapes of thevacuum pad and the protrusion pins will be developed on the reflectivefilm (73), thus seriously affecting the yield in the production of thereflector plates.

The problem of reflections from the exposure stage which will affect theyield rate of reflector plate output will have to be corrected.

SUMMARY OF THE INVENTION

The main object of the present invention is to provide a method forfabricating reflector plates of a reflective liquid crystal display thatcan prevent abnormal reflection from the exposure stage during theformation of the undulating resin outgrowth, thus it can preventabnormal pattern marks occurring over the reflective surface, shortenthe exposure time in the lithography process and improve the yield ratein the production of reflector plates.

The method for fabricating reflector plates of a reflective liquidcrystal display comprises the steps of:

forming transparent electrodes after thin film transistors are built ontop of a glass substrate;

depositing a protection layer over the transparent electrodes forshielding off light reflection from the exposure stage;

patterning the transparent electrodes and the protection layer to definethe pixel grid through the steps of:

spin coating a photo-resist layer over the protection layer with polymerresin material;

removing resin materials in non-pattern areas of the photo-resist layerby light exposure and developing with a developing solution; and

depositing a reflective film over the polymer resin.

In the above-mentioned fabrication process, the protection layer iscreated in advance of the undulating resin outgrowth; therefore it caneffectively prevent reflection from the exposure stage that causesabnormal pattern marks on the reflective surface due to uneven exposure.The above-mentioned fabrication process applies to a reflective typereflector plate.

In the case of a semi-transmissive type reflector plate, after finishingthe reflective film, there should be a photo etching process to removethe metal deposits over non-pattern areas to form a light-transmittingregion on the reflective film.

The secondary object of the present invention is to create a protectionlayer in the pixel region at the same time as the formation of the thinfilm transistors on the glass substrate, so as to shield off reflectionfrom the exposure stage during the lithography process and thedevelopment of uneven reflective surface.

The features and structure of the present invention will be more clearlyunderstood when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a˜d are the fabrication process of a reflective type reflectorplate as implemented in the first embodiment;

FIGS. 2 a˜d are the fabrication process of a semi-transmissive typereflector plate as implemented in the second embodiment;

FIGS. 3 a˜c are the fabrication process of a reflective type reflectorplate as implemented in the third embodiment;

FIGS. 4 a˜c are the fabrication process of a semi-transmissive typereflector plate as implemented in the fourth embodiment;

FIGS. 5 a˜c are the fabrication process of a reflective type reflectorplate as implemented in the fifth embodiment;

FIGS. 6 a˜c are the fabrication process of a semi-transmissive typereflector plate as implemented in the sixth embodiment;

FIGS. 7 a˜c are the conventional fabrication process for asemi-transmissive type reflector plate of display device; and

FIGS. 8 a˜c are the conventional fabrication process of a reflectivetype reflector plate of display device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will hereinafter be described in reference to thesix embodiments and the drawings. The fabrication process includes thesteps of:

forming transparent electrodes after thin film transistors are built ontop of a glass substrate;

depositing a protection layer over the transparent electrodes forshielding off light reflection from the exposure stage;

patterning the transparent electrodes and the protection layer to definethe pixel grid, which is performed through a series of processes:

spin coating a photo-resist layer over the protection layer;

removing the resin materials in the non-pattern areas of thephoto-resist layer by light exposure and development; and

depositing a single or multiple layer reflective metal film.

This fabrication process starts with the pre-formation of a protectionlayer on the glass substrate in advance of the undulating resinoutgrowth, thus enabling effective shielding of reflection from theexposure stage during lithography, which results in abnormal patternmarks occurring on the reflective surface due to uneven exposure.

The formation of transparent electrodes (11), as shown in FIG. 1A, it isperformed after thin film transistors are built on top of a glasssubstrate (10), so that a pixel region is formed in between the glasssubstrate (10) and the transparent electrodes (11) have a gateinsulating layer (101) and a protective layer (102).

The forming of a protection layer (12), metal or non-metal, as shown inFIG. 1 b, on the surface of the transparent electrodes (11) to shieldoff light reflection from the exposure stage during lithography. In thepresent embodiment the metal material used in the process is molybdenumalloy, or could be other metals such as AL, Cr, Cu, Co, Mo, Ti, W, Sn,Pb, Ag, Au, Ni, or Zr.

The patterning of the transparent electrodes (11) and the protectionlayer (12) is performed through the process of spin coating of the photoresist layer (13) over the protection layer (12) using polymer resinmaterial, as shown in FIG. 1 c; exposure with a photomask anddevelopment with a development solution to remove the resin materialover the non-pattern areas.

The deposition of a single or multiple layers of reflective metal film(14) as shown in FIG. 1 d, is in accordance with the masked pattern. Inthe present embodiment, the reflective metal film (14) is formed by athree-layer film structure, composed of Molybdenum alloy, aluminum, andthen Molybdenum alloy;

FIGS. 2 a˜c show the fabrication process to produce a semi-transmissivetype reflector plate. The basic steps are identical to those used forthe reflective type reflector plate, including deposition of thetransparent electrodes, patterning the transparent electrodes and theprotection layer, deposition of a photo-resist layer, exposure anddevelopment, and deposition of the reflective metal film, as shown inFIGS. 2 a˜c. However, in order to achieve partial light transmissionthrough the reflector plate, there is an etching back process after thedeposition of the reflective metal film, as shown in FIG. 2 d, to removesome of the metal deposits on the protection layer (12) to create alight-transmitting region (15).

The present invention as it applies to the fabrication reflective typereflector plate and semi-transmissive type reflector plates in severalof the preferred embodiments is more advantageous over the conventionalmethod, which will be explained below:

Prevention of abnormal pattern marks occurring on the reflectivesurface: the protection layer enables light projections to be scatteredevenly over the reflection surface of the protection layer, not in theregular reflection direction. Since the protection layer (12) is createdin advance of the undulating resin outgrowth, the protection layer (12)can effectively shield off the reflections from the exposure stage, thusno image of the vacuum pad and the protruding pins will appear on thereflective surface., thus there will be no abnormal pattern marks on thereflective surface, and the yield rate of the reflector plate can alsobe improved.

Shortening the exposure time during lithography: the conventionalprocesses use polymer resin material with low photosensitivity and thickbody. The low photosensitivity resin could prolong the exposure time,and the thick body resin could cause uneven light exposure. However, inthe present invention, highly photosensitive resin is used to shortenthe exposure time, and the protection layer enables light projections tobe scattered evenly over the surface of the protection layer, thus thenecessary exposure time of the polymer resin can be shortened. Forundulating resin without the protection layer, the light exposure timeis about 120 mJ, but with the protection layer the light exposure timeduration only takes 60 mJ. The light exposure time is shortened by asmuch as 50%, thus improving the output yield.

The present invention can be implemented with other fabricationprocesses besides those disclosed in the embodiments above:

FIG. 3 shows the fabrication process of a reflective type reflectorplate as implemented in the third embodiment, which enables thereflective film to be formed at the same time as the thin filmtransistors over the glass substrate (10). Then, an undulating resinoutgrowth is built over the reflective film.

The thin film transistors are first created on the glass substrate (10),then the gate electrodes, the gate insulating layer, and the protectivelayer are formed in that order. In the present embodiment, theprotection layer in the pixel region is formed at the same time as theformation of the gate electrodes, through unified patterning for themetal interlayers, in the process of forming the thin film transistors.The advantages are that all the characteristics in the previousembodiment can be retained.

FIG. 3 a shows the fabrication process of a full reflector plate asimplemented in the third embodiment. During the formation of thin filmtransistors on the glass substrate (10), a protection layer (12) isformed at the same time as the gate insulating layer (101) in the pixelregion. Then, the sequence of steps, as shown in FIGS. 3 a˜c, areperformed over the glass substrate (10): deposition of the transparentelectrodes, patterning of the transparent electrodes, deposition of thephoto-resist layer, exposure and development, and deposition of thereflective metal film, to complete the fabrication of a full reflectorplate.

FIG. 4 shows the fabrication process of semi-transmissive type reflectorplate in the fourth embodiment, which is basically identical to that ofthe third embodiment, with the addition of an etching back process tocreate the light-transmitting region.

FIG. 5 shows the fabrication process for a transmissive type reflectorplate in the fifth embodiment. The process steps largely resemble thoseused in the third and fourth embodiments in that the part of protectionlayer is formed at the same time as the thin film transistors, but thedifference is that the source/drain electrodes and the protection layerare formed at the same time in the process of forming the thin filmtransistors through unified patterning. It can be seen, from FIG. 5 a,after the thin film transistors are built on top of the glass substrate(10), a protection layer (12) is formed at the same time as the gateelectrodes in between the gate insulating layer (101) and the protectionlayer (102) the protection layer (12). Subsequent steps in thefabrication process, as shown in FIGS. 5 a˜c, are to be performed overthe glass substrate (10) in the order of: deposition of the transparentelectrodes, patterning of the transparent electrodes, spin coating ofthe photo-resist layer, exposure and development, and deposition of thereflective metal film. This process is for fabrication of a fullreflector plate.

FIG. 6 shows the fabrication process for a semi-transmissive typereflector plate in the sixth embodiment, wherein the only difference inthe fabrication process versus the fifth embodiment is the addition ofan etching back process to form the light-transmitting region.

The foregoing description of the preferred embodiments of the presentinvention is intended to be illustrative only and, under nocircumstances, should the scope of the present invention be sorestricted.

1. A method for fabricating a reflective type reflector plate of areflective liquid crystal display, the method comprising the steps of:preparing a glass substrate with thin film transistors built on asurface of the glass substrate; forming transparent electrodes over theglass substrate after the thin film transistors are built on the glasssubstrate; depositing a protection layer over the transparentelectrodes; patterning the transparent electrodes and the protectionlayer to form pixel patterns; spin coating a photoresist layer over theprotection layer using polymer resin material; removing the photoresistlayer over non-patterned areas; and depositing a reflective metal filmover the photoresist layer retained on the glass substrate; whereinafter the protection layer is deposited over the transparent electrodes,the protection layer shields undesired reflection light during anexposure stage and reduces the exposure time.
 2. The method as claimedin claim 1, wherein the protection layer is metal material.
 3. Themethod as claimed in claim 1, wherein the protection layer is non-metalmaterial.